Another Perspective on Entrapment
I teach aquatic safety — suction outlet entrapment avoidance, to be exact In reading the article in the Feb.29th issue (“Bill Proposes Change to California Pool Law, page 12), I saw a photo of an anti-vortex main drain cover. The caption under that photo stated “Legal glitch":Currently, a California law requires an anti-entrapment drain cover be added when any home improvement permit is pulled. The photo would lead one to believe the cover shown to be a anti- entrapment type cover,  that is indeed a misnomer. The photo is an anti-vortex type cover, (I do understand the term “journalistic license.”)

Perhaps I can help make this more clear by explaining the difference between the two different items. Please note: This could be a matter of a safe dual drain system or a deadly dual drain system.

Back in the early 1970s, due to the advent of closed impellers and self-priming pumps, more powerful suction outlets and main drains came out. To prevent air from being entrained into the main drain via a vortex, anti-vortex main drain covers were developed
— not so much to protect children, but to protect pump shaft seals and motors. Safety was not the issue because suction entrapment was not “in the news” at that time.

One of the criteria of the anti-vortex cover was “a small open surface area” perhaps 10 square inches or less. These covers did, indeed, protect pump motors and the related seals, but not children. The turbulent area around the small open surface area created a high velocity that could pull in hair or bathing suit ties, etc., and in some cases harbored a finger entrapment potential.

Then in the late 1970s, we had child injuries and worse incidents making the news. Finally, in 1995, the first child anti-entrapment type cover was invented. The inventor (Harry Newhard) realized a larger open surface area meant less velocity and a slower flow rate through the cover would prevent hair entanglement. His invention was deemed an “anti-entrapment type main drain” cover because it was created to reduce child entrapment injuries or worse.

Also in the late 1970s, studies were being done to use dual drain technologies to prevent child entrapment. These tests were done mostly on 12 inch by 12 inch main drains. The individual could “roll off’ the 96-square-inch open surface area and release himself. Remember, we are dealing with open surface area, not overall area. Open surface area on some 12-by-12-inch grates measures 96 square inches, and the overall area of 144 square inches. More testing should have been done with smaller sumps.

Now 2007 arrives and we’re recommending hydraulically balanced dual drains separated by a minimum of 3 feet. Unfortunately, this may not be as safe as it seems. It is important we remember the “small open surface area” of some covers.

Here is an example: We have a code-compliant dual drain system; we also have two ANSI/ASME 112.19.8 Standard-certified anti- vortex drain covers with a
small open surface area of approximately 8 inches, Now, for whatever reason, one drain cover becomes missing or dislodged. That open main drain pipe or sump can now have a hold-down force that could preclude a child’s escape. In other words, he is trapped to the forces from the pump suction under him and the weight of the water above him as well, the opposing drain cover (still intact) is allowing the pump to maintain a full head and hold the child to the unprotected suction outlet. A bad scenario, I know.

To recap: 1970 main drain cover, 1980 anti-vortex cover, 2000 anti-entrapment cover and now 2007 anti-entrapment type suction outlet cover
As we build more and more dual drain systems, we need to understand the hydraulics involved. It would be far more beneficial to install large open surface area anti-entrapment type suction outlet covers to minimize the related suction hazards as well as allowing the pumps to operate with more fluid volume at a lower velocity. (Note: The connecting pipe between the dual drain sumps should be 2.5 inches in diameter or larger, not to exceed 6 feet in separation to avoid high hold-down forces.)
Bottom line: It boils down to child safety. We need to focus on protecting children, and understand how systems and products relate to each other — not just blindly install systems and products without understanding the reasoning behind their development or effects after installation and operation. We require education to be effective in our safety related efforts.

Thank you for promoting child aquatic safety. Please keep up the good work and, perhaps increase your photo budget.

 

 

Ron Schroader
Aquatic Safety Consultant
New Water Solutions Inc. Lake Worth, Florida.

 

 

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New Water Solutions, Inc., Drainsafe drainsafe.com nor I, Ron Schroader recommend the use of one product or device over another.
 Products must be implemented as per system/job specific application . It is the obligation of the installer to understand the intended use and application prior to installation of any product or device.
We do however recommend the use of products certified via (NRTL) Nationally Recognized Testing Laboratories as per ASME/ANSI A112.19.17 & ASME/ANSI A112.19.8 2007 Standards.
 All products must be installed as per manufacturers instructions and be job site specific to meet the criteria of each individual application.
 

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